Various types of analytical tests related to patient diagnosis and therapy can be performed by analysis of a liquid sample taken from a patient's infections, bodily fluids or abscesses. These assays are typically conducted with automated clinical analyzers onto which tubes or vials containing patient samples have been loaded. The analyzer extracts liquid sample from the vial and combines the sample with various reagents in special reaction cuvettes or tubes. Usually the sample-reagent solution is incubated or otherwise processed before being analyzed. Analytical measurements are often performed using a beam of interrogating radiation interacting with the sample-reagent combination to generate turbidimetric, fluorometric, absorption readings or the like. The readings allow determination of end-point or rate values from which an amount of analyte related to the health of the patient may be determined using well-known calibration techniques.
An important contributor to maintaining a high efficiency in throughput of patient samples is the ability to quickly and securely introduce a plurality of samples to the sample testing portion of an analyzer. Patient samples are typically held in a container such as a test tube, and the tubes placed into a sample rack adapted to support multiple sample containers generally in an upright orientation.
The sample rack is usually placed in an input portion of the analyzer and then moved to a location where a portion of the liquid patient sample is extracted, usually by aspiration using a hollow, needle like probe from the sample container for testing in the analyzer, Afterwards, the sample rack may be moved to temporary storage area or to an output portion of the analyzer where the user can conveniently remove the sample rack from the analyzer See for example,
Patient samples are known to be provided to such analyzers in a large number of different types of tubes: 13 mm and 16 mm diameter tubes are popular as are “small sample” tubes, sometimes called sample cups, and tubes are also used having varying heights. After being placed on the analyzer, a predetermined, known portion of the original sample is aspirated from the tube and analytical tests conducted thereon. Sample racks with features for accommodating different types of tubes may be found in U.S. Pat. Nos. 5,687,849; 5,378,433; and 4,944,942 and an adapter for accommodating different types of tubes may be found in U.S. Pat. No. 5,985,219,
A problem with aspirating sample from a small sample cup arises because the “dead volume” of sample remaining between the bottom of an aspiration probe and the bottom of the small sample cup comprises a large portion of the total sample volume. Uncertainties concerning the exact location of the bottom of the small sample cup prevent positioning the bottom of the probe precisely at the bottom of the small sample cup. Therefore, when a small sample cup is presented to an aspiration probe, the aspiration process is unable to access the total volume of sample within a small sample cup. For obvious reasons, it would be highly desirable to have a device that would automatically enable an aspiration probe to contact the bottom of a small sample cup regardless of the height location of the bottom of that small sample cup.